Removal of scale and rust from iron and steel



yaw w No Drawing. on

Patented Oct. 9, 1923.

UNITED STATES To all whom it may concern:

Be it known that I, HARRY N. HoLMns, a citizen of the United States, residing at Oberlin, in the county of Lorain and State of Ohio, have invented certain new and useful Improvements in Removal of Scale and Rust from Iron and Steel, of which the following is a specification.

This invention relates to the removal of scale and rust from iron or steel. The invention is particularly applicable for the pickling of iron or steel wire or sheets in mill practice, but is also useful in many other ways, such as for cleaning or freeing iron or steel in any form from rust or oxides,

or for removing scale such as bilegsgle or the like from sheets or tubes. .v

One important feature of the invention is the provision of a pickling bath of proper composition and strength and its use under such conditions as will very materially inhibit if not wholly prevent any attack of the iron or steel base by the pickling bath, but without material inhibition of the attack of the bath on rust, or oxides or scale to be removed.

According to my invention the metal is pickled in a bath of suitable acid containing a proper quantity of the inhibiting agent, which may be one of the alglehydes. The presence of a relatively small quantity of an aldehyde in an acid solution is found to inhibit greatly or prevent any attack of the acid upon the base metal but not to prevent or inhibit its attack upon oxides, carbonates, or like materials, such as rust or scale. If the acid solution is sufficiently strong-the inhibiting agent, such as an aldehyde, is effective at temperatures above normal or atmospheric, such as temperatures up to 50 C. or even (1., so that according to common mill practice the bath may be used at temperatures above normal with a very material increase above normal in the rate of rust or scale removal, whereas if the acid is weak the inhibiting agent appears to lose its effectiveness above normal temperatures. Consequently relatively strong acid solutions are preferable, although no additional expense in the acid is entailed because the acid attacks the rust or scale and is ineffective upon the base metal.

The acid may be of any of the ordinary acids commonly used for pickling purposes but also is naturally a gagid ghims not HARRY N. HOLMES,

Application filed January 17, 1921.

II- M PATENT OFFICE.

OF OBERLIN, OHIO.

REMOVAL OF SCALE AND RUST FROM IRON AND STEEL.

Serial No. 437,995..

emufifithe aldehyde. For this reason nitric or ot er so-called oxidizing acids are not suitable for use, as they probably attack the aldehyde and so oxidize it as to minimize or destroy its inhibiting effect. Examples ofsuitable acids are sulphuric, hydrochloric, phosphoric, and even acetic or some of the similar weaker or organic acids, although these weaker acids would probably not be sufliciently effective for commercial mill practice.

The acid used can be of any suitable strength with due regard to the facts above noted, to-wit, the loss of effectiveness of the inhibiting agent at higher temperatures when the acid is relatively weak. In practice I have produced useful effects with sulphuric acid solutions made up in the proportions of eleven parts of water to one part of commercial concentrated sulphuric acid by volume. \Vith such solutions containing the inhibiting agent hereafter referred to there is no appreciable effect of the acid upon the base metal. While the oxide or scale is attacked and removed the rate of attack is probably too slow for ordinary mill practice and at higher temperatures, say above 40 or 50 C. the inhibiting effect decreases so as to be practically nil. For these reasons I prefer to use an acid of a proximately the strength of one part of acid to five of water by volume. With this solution the inhibiting effect is not only pronounced when the solution is cold or at normal temperatures, but is also so pronounced as to be of practically full value at the temperatures used in mill practice, say 80 C. Hydrochloric acid solutions can be used in various strengths, for example, one volume of commercial concentrated acid to one volume of water, the inhibiting effect being maii ifitaiirileildbat the higher temperature nfoted.

e i i itin agent may be any 0 the aldeh des but o f course is chosen with regard to the cost of material. Good effects have been noted with formaldehyde (the so-called 40% formalin solution) hen; zaldehyde, f lift and acetaldehyde. Acetaldehyde being very volatile would probamy be used as the solid, aldehyde ammonia. Other aldehydes are also probably useful. Referring particularly to formaldehyde I find that this material is effective in a pickling bath in relatively small quantities. For example, in a sulphuric acid bath of the dilu- Fifi tion of five parts of water to one of commercial concentrated acid by volume the forialin solution above referred to may be dded in the proportion of as low as onei one per cent by volume. Larger tiimounts tian may be employed 11112; tired, but without appearing to materially affect afii iij figfjue"inia g eiag gfi'as, so h fidQiQQllfiLmaterial is to some extent 10 wasted.

My improved pickling bath enables a base of iron or steel in the form of wire, sheets or the like to be readily and quickly freed of rust, oxide, scale or carbonates by a treatment that can be carried on with as great rapidity as the process, as now in use. butwithout danger of material attack upon the material. The invention therefore involves a material saving not only in the bath but also in the base metal.

What I claim is:

1. The method of removing rust or scale from iron or steel, consisting in pickling the same in an acid bath containing at least one fifth of 1% by volume of an aldehyde to inhibit the attack of the acid upon the base metal.

2. The method of removing rust or scale from iron or steel, consisting in pickling the same in an acid bath containing at least onefi'tth of 1% by volume of formaldehyde to inhibit the attack of the acid upon the base metal.

8. The method of removing rust or scale from iron or steel consisting in pickling the same in a bath of sulphuric acid containing at leastone-fifth of 1% by volume of an aldehyde? 4. The method of removing rust or scale from iron or steel consisting in pickling the same in a bath of sulphuric acid containing at least one-fifth of 1% b volume of formaldehyde.

In testimony whereof I hereby afiix my signature.

HARRY N. HOLMES. 

